The major smooth muscle organs of the body include the gastrointestinal (GI) tract organs, the urinary bladder, and the uterus. The motor activity associated with these organs is essential in many physiological processes such as digestion, excretion and parturition. Many pathologies arising from impaired smooth muscle motor activity are known. In the GI tract, for example, smooth muscle dysfunction is a common pathology often making life for those suffering from it uncomfortable and painful.
The electrical activity of smooth muscle may consist of two components: slow waves and action potentials. Slow waves are periodic, spontaneously generated, low frequency signals. Characteristic frequency ranges of the slow wave of some GI tract organs are shown in Table 1. Slow waves propagate throughout the body and may be detected using electrodes disposed far from the wave source. Since the slow waves of the various smooth muscle organs have different characteristic frequency ranges, the slow waves generated by different organs can be resolved from the obtained signal by spectral analysis. No correlation exists between slow waves and motor activity. Thus, slow waves may be detected in the various GI tract organs during periods of motor activity as well as during periods of quiescence. Indeed, slow waves occur in the GI tract even in the absence of any motor activity such as in cases of gastro or intestinal paresis.
Smooth muscle contraction is always accompanied by a burst of action potentials and the generation rate of the action potentials per unit volume muscle tissue is proportional to the generated contractile force. An action potential burst, and hence contraction, can occur only on the crest of a slow wave, so that slow waves are involved in the timing of smooth muscle contraction. Slow waves also synchronize smooth muscle contraction, for example, along the GI tract. This gives rise to the migrating myoelectrical complex (MMEC) in which a region of muscle contractions migrates along the GI tract from the stomach to the ileum. Unlike slow waves, however, the propagation distance of an action potential is very short (several millimeters). Therefore, action potentials, and hence motor activity, are detected only with electrodes implanted in the wave source. In order to monitor action potentials along the entire GI tract, several electrodes implanted along the length of the GI tract must be used.
Russian Patents Nos. 2,088,147; 2,095,020; 2,054,885; 2,044,513; 2,623,419 and SU 1,124,919 disclose recording the electrical activity of the GI tract using cutaneous electrodes placed on body extremities. The signal is filtered to remove components not arising from the GI tract and a power spectrum of the filtered signal is obtained. Since the slow waves of the various GI tract organs (stomach, duodenum, jejunum, ileum) have non-overlapping, characteristic frequency ranges (Table 1), each peak in the power spectrum can be associated with (a different GI tract organ. These methods detect slow waves of the GI tract organs but not action potentials. Since it is the action potential burst and not the slow wave that is correlated with motor activity, these methods do not provide any information on GI tract motor activity. These methods, therefore, have not found much use in practice.
TABLE 1Basic frequencies (Hz) of the slow waves ofsome gastrointestinal tract organsOrganHumanDogStomach0.05-0.080.04-0.09Duodenum0.19-0.210.29-0.35Jejunum0.165-0.19 0.25-0.29Ileum0.133-0.1650.20-0.25